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J. Exp. Med.,
Volume 186, Number 12, December 15, 1997 2033-2038
By
From the Ludwig Institute for Cancer Research, Lausanne Branch, University of Lausanne, 1066 Epalinges, Switzerland
Using H-2Kd-restricted photoprobe-specific cytotoxic T lymphocyte (CTL) clones, which
permit assessment of T cell receptor (TCR)-ligand interactions by TCR photoaffinity labeling,
we observed that the efficiency of antigen recognition by CTL was critically dependent on the
half-life of TCR-ligand complexes. We show here that antigen recognition by CTL is essentially determined by the frequency of serial TCR engagement, except for very rapid dissociations, which resulted in aberrant TCR signaling and antagonism. Thus agonists that were efficiently
recognized exhibited rapid TCR-ligand complex dissociation, and hence a high frequency of
serial TCR engagement, whereas the opposite was true for weak agonists. Surprisingly, these
differences were largely accounted for by the coreceptor CD8. While it was known that CD8
substantially decreases TCR-ligand complex dissociation, we observed in this study that this
effect varied considerably among ligand variants, indicating that epitope modifications can alter
the CD8 contribution to TCR-ligand binding, and hence the efficiency of antigen recognition
by CTL.
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